Connected: An Internet Encyclopedia
RFC 1123 - 5.2 PROTOCOL WALK-THROUGH

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### 5.2 PROTOCOL WALK-THROUGH

This section covers both RFC-821 and RFC-822.

The SMTP specification in RFC-821 is clear and contains numerous examples, so implementors should not find it difficult to understand. This section simply updates or annotates portions of RFC-821 to conform with current usage.

RFC-822 is a long and dense document, defining a rich syntax. Unfortunately, incomplete or defective implementations of RFC-822 are common. In fact, nearly all of the many formats of RFC-822 are actually used, so an implementation generally needs to recognize and correctly interpret all of the RFC-822 syntax.

5.2.1 The SMTP Model: RFC-821 Section 2
5.2.2 Canonicalization: RFC-821 Section 3.1
5.2.3 VRFY and EXPN Commands: RFC-821 Section 3.3
5.2.4 SEND, SOML, and SAML Commands: RFC-821 Section 3.4
5.2.5 HELO Command: RFC-821 Section 3.5
5.2.6 Mail Relay: RFC-821 Section 3.6
5.2.7 RCPT Command: RFC-821 Section 4.1.1
5.2.8 DATA Command: RFC-821 Section 4.1.1
5.2.9 Command Syntax: RFC-821 Section 4.1.2
5.2.10 SMTP Replies: RFC-821 Section 4.2
5.2.11 Transparency: RFC-821 Section 4.5.2
5.2.12 WKS Use in MX Processing: RFC-974, p. 5
5.2.13 RFC-822 Message Specification: RFC-822 Section 4
5.2.14 RFC-822 Date and Time Specification: RFC-822 Section 5
5.2.15 RFC-822 Syntax Change: RFC-822 Section 6.1
5.2.16 RFC-822 Local-part: RFC-822 Section 6.2
5.2.17 Domain Literals: RFC-822 Section 6.2.3
5.2.18 Common Address Formatting Errors: RFC-822 Section 6.1
5.2.19 Explicit Source Routes: RFC-822 Section 6.2.7

Next: 5.2.1 The SMTP Model: RFC-821 Section 2

Connected: An Internet Encyclopedia
RFC 1123 - 5.2 PROTOCOL WALK-THROUGH